The present invention relates to methods and apparatus for casting a molten material in a mold which includes a foam-plastic pattern embedded in a binderless granular material such as a suitable sand. The molten material is poured into the space occupied by this foam-plastic pattern, and the pattern upon being contacted by the molten material decomposes, as by being burned away, while at the same time a gas is generated. The foam-plastic pattern becomes replaced by the molten material which thus assumes the configuration of the pattern in the mold.
It is already known to manufacture castings by embedding a foam-plastic pattern in a loose, binderless sand and then replacing the pattern with a molten material such as a molten metal which burns away the pattern with a gas being generated during replacement of the pattern by the molten material. Thus, suitable foam-plastic patterns made of polyurethane or polyvinylchloride have conventionally been embedded in a binderless loose sand with the molten metal being poured into the space occupied by the pattern so as to replace the latter.
Methods and apparatus of this type have the disadvantage of being capable of producing only castings of simple configuration. The reason for this is that the binderless granular material in which the foam-plastic pattern is embedded has only a limited firmness or stiffness which is insufficient to permit complex configurations to be cast. For these reasons a method and apparatus of the above type has not been widely used in connection with the manufacture of castings of complex configuration having undercuts which open outwardly or having hollow interior spaces.